The present invention relates to an electro-optical distance measuring instrument, by which receives a reflection light from an object to be measured and performs a distance measurement.
A surveying instrument such as a laser scanner, a total station, or the like has an electro-optical distance measuring instrument for detecting a distance to an object to be measured by a prism distance measurement using a reflection prism and a non-prism distance measurement without using the reflection prism.
In the electro-optical distance measuring instrument, an optical path splitting component is disposed on a projection optical axis. By the optical path splitting component, a distance measuring light is reflected and projected, further a reflected distance measuring light from the object to be measured is passed through, a light receiving optical system receives the reflected distance measuring light, and a distance measurement is performed.
In a conventional electro-optical distance measuring instrument, a partial transmission coating is formed at a central part of the optical path splitting component, and the central part is designed as a beam splitter. Further, an antireflection coating (an AR coating) is provided at a part other than the central part, and the part other than the central part is designed as a full transmission part. In such electro-optical distance measuring instrument, the reflected distance measuring light passes through the full transmission part and is received by the light receiving optical system, and the distance measurement is performed. Further, a part of the central part of the reflected distance measuring light also passes through the beam splitter and is received by the light receiving optical system.
As described above, the central part of the optical path splitting component is the beam splitter, and the part of the central part of the reflected distance measuring light passes through the beam splitter and enters the light receiving optical system. Therefore, even at a short distance measurement, the reflected distance measuring light with a light amount which may not cause a trouble in a measurement can be received.
However, in a case of the electro-optical distance measuring instrument with the optical path splitting component, in which a beam splitter is provided at the central part, all of the reflected distance measuring lights which enter a condenser lens of the light receiving optical system need to pass through the optical path splitting component. Therefore, the optical path splitting component becomes large, and an increase in size of an optical system is unavoidable. Further, a weight is also increased according to the increase in size.